Sepsis is a toxic condition resulting from the spread of bacteria or their products from a focus of infection, especially septicemia. According to the Centers for Disease Control (CDC), septicemia is a leading cause of death in the United States, especially among the elderly. Death can occur in 40% to 60% of the patients with septicemia. It has been estimated that some five hundred thousand cases of sepsis occur annually in the United States. Accordingly, methods for detecting conditions indicative of sepsis would have significant use in medical practice.
Currently, sepsis remains an elusive therapeutic target. Pharmaceutical companies have developed potential therapeutics for action against sepsis-causing bacterial components and against chemical signaling molecules in inflammatory and coagulation pathways. Agents such as monoclonal antibodies and antagonists of tumor necrosis factor (TNF) have been developed for treatment of sepsis, but not with great success. Scavengers of nitric oxide (NO) have also been proposed since nitric oxide has been implicated as a mediator in the inflammatory cascade that leads to shock. Coagulation pathway molecules such as LACI or TFPI have been developed for treatment of sepsis and septic shock as disclosed, e.g., in PCT International Applications WO 93/241,143, published Dec. 9, 1993, and WO 93/252,230, published Dec. 23, 1993. Most recently a human-activated protein C, which is a vitamin K dependent protein of blood plasma, has been produced by recombinant DNA and reported to be clinically studied with effective results against sepsis, Bernard et al., New England Journal of Medicine, Vol. 344, pp. 699-709, March 2001. The latter drug has been designated with the name “Xigris.”
For treatment of sepsis, good identifying or diagnostic markers to predict which patients can benefit from therapy and to monitor the response to treatment during infection are in great need.
Oxidants are thought to be key components of the neutrophil host defense system (ref. 1). Upon contact with a pathogen, neutrophils produce a respiratory burst characterized by intense uptake of oxygen. The resulting superoxide dismutates into hydrogen peroxide (H2O2) (ref. 2). The toxicity of H2O2 is greatly enhanced by the heme enzyme myeloperoxidase, which uses H2O2 to convert chloride (Cl−) into hypochlorous acid (HOCl) (refs. 3-8).Cl−+H2O2+H+→HOCl+H2ORemarkably, myeloperoxidase is the only mammalian enzyme known to oxidize Cl− to HOCl at plasma concentrations of halide (refs. 3-6).
Chloride is considered the major halide used by myeloperoxidase. Bromide (Br−) has attracted little attention because its extracellular concentration is at least 1,000-fold lower than that of Cl− (plasma [Cl−] 100 mM, plasma [Br−] 20-100 μM) (ref. 9). However, brominating intermediates such as HOBr are also potent antimicrobial oxidants in vitro (refs. 10,11).
It has been recently demonstrated that myeloperoxidase can both chlorinate and brominate nucleobases at plasma levels of halide (ref. 12). In the reaction pathway, myeloperoxidase initially produces HOCl, which reacts with Br− to generate brominating intermediates (ref. 12). It has not been established heretofore whether this brominating pathway is physiologically relevant.
It also has not been known heretofore whether the myeloperoxidase system is cytotoxic to bacteria in vivo, though myeloperoxidase-deficient mice are susceptible to fungal infection (refs. 13,14).